I suggested these a while ago but I though I might as well re suggest them

1. Double Cubelets - for a day or two after reaching the vote goal cubelets collected are doubled.

2. Xp Multiplier - multiplies the xp you get for a couple days after the goal is reached.

3. Special Events - possibly make some special extreme versions of games that are only available for a day upon voting rewards being released. This could be like versions of the game that simply has a ton of players in them or even return of games like Ender for a short time (though other games would probably be preffered.)

4. Going off of special events you could also simply do developer Q&A livestreams or a "come play with all the staff /owners" day not really a great idea but its there now have the cube community livestreams

5. Allow all cosmetics for all players for a day after goal is reached.

6. Rank Giveaway - After a goal is reached give out a rank to a random player either via twitter or another in game method.

7. Everything Unlocked for a day - simply put after a goal is reached every player has access to every kit/ability/tower for a day

That's all I can think of for now if you have any ideas/thoughts/opinions leave then below

Edit: you could also have multiple voting goals which do a different one of these each time probably ending with a special event after an insane amount of votes

I think it would be funny if for 5 minutes after a vote goal is reached everyone could vote in eggwars skywars etc. Donators votes during that time would count triple and they get doubled cubelet chance and double chance to get something rare inside a cubelet.